1. Field of the Invention
The present invention relates to an optical scanning apparatus for use in a radar apparatus, a display apparatus and the like, and an optical reflection device used for the same optical scanning apparatus.
2. Description of the Related Art
A vehicle-mounted radar apparatus to scan a beam of light emitted from a light source of laser, an LED or the like in two axial directions perpendicular to each other and a projection type display apparatus have been put to practical use. These optical scanning apparatuses are each configured to include a light source, and, for example, an actuator and its drive control apparatus as shown in FIG. 13.
The actuator is configured to include a reflective device that makes a reflecting part pivot in two operating axes perpendicular to each other, and driving parts that determine the drive frequencies of the reflecting part.
In particular, when drawing a trace by scanning a beam of light by Lissajous scanning, the trace and a period (hereinafter, referred to as a “Lissajous period”) for which the trace returns to the former trace are determined by the drive frequencies of the axes. In a radar apparatus or a projection type display apparatus, a beam of light is required to pass over all pixels defined by a resolution or the like within a time defined by a frame rate or the like. For the above purpose, it is required to set the Lissajous period to an appropriate value and is set the drive frequencies so that the trace becomes as precise as possible.
In the actuator drive control apparatus of the first prior art shown in FIG. 13, the mesh count of the trace drawn by scanning a beam of light on the projection plane is preliminarily set in a predetermined range, the clock count of an oscillator 51 and the actual resonance frequencies of two operating axes (operating axes driven by a first movable part 54 a second movable part 55) of a scanner 53 obtained by resonance frequency setting means 52 are inputted to a drive frequency setting means 56, and drive frequencies of the highest operating efficiency are calculated. As prior art document information relevant to the invention of this application, for example, Patent Document 1 has been known.
Moreover, the optical scanning apparatus of a second prior art for use in a projection type display apparatus or the like is configured to include a mirror part that reflects a beam of light emitted from a light source, a first movable part that supports the mirror part by a first torsion bar inside a first frame, and a second movable part that supports the first movable part by a second torsion bar inside a second frame substantially perpendicular to the first torsion bar, by which the mirror part pivots around the two axes by a Coulomb force, a Lorentz force and a piezoelectric displacement applied to the first and second movable parts. As prior art document information relevant to the invention of this application, for example, Patent Document 2 has been known.
Prior Art Documents of patent documents related to the present invention are as follows:    Patent Document 1: Japanese patent laid-open publication No. JP 2004-302104 A; and    Patent Document 2: Japanese patent No. JP 2722314.
In the actuator drive control apparatus of the first prior art acquires the drive frequencies with which the desired resolution is obtained in consideration of deviations in the actual resonance frequencies, and the resolution largely fluctuates depending on the frame rate in the case of Lissajous scanning.
Moreover, in the drive control apparatus of the second prior art, it is desirable to make the drive frequencies coincide with the resonance frequencies of the respective operating axes in order to improve the driving efficiency of the mirror part. However, since the actual resonance frequencies fluctuate depending on variations in shape in the manufacturing processes and environmental factors of ambient temperature changes and so on, it is required to correct the drive frequencies in consideration of these fluctuations.